STABLE ISOTOPES OF HYDROGEN AS AN ENVIRONMENTAL INDICATOR FOR LANDFILL LEACHATE

The unique stable hydrogen isotopic signature of landfill leachate can be used as a tracer for identifying impact on local groundwater. Leachate solution is generated by a combination of waste dewatering and interaction of waste with meteoric precipitation. Modern landfills control leachate impact with liners that include systems for collection of leachate for treatment and disposal. However, all liners are prone to tearing during installation and may otherwise eventually fail, leading to contaminant release into underlying aquifers. The chemical composition of landfill leachate is highly variable, making interpretation of monitoring well data and identification of leachate in groundwater difficult.

Generation of methane gas during anaerobic decomposition of organic waste produces isotopically light methane, leaving the water enriched in the heavier hydrogen isotope. The methanogenesis process does not affect the oxygen isotopic composition. We evaluated the isotopic composition of landfill leachate collected over multiple years from a municipal landfill. The Dyer Boulevard Landfill is a 164-hectare complex in Palm Beach County, Florida, located on the southeast coast of the Florida peninsula. Compared to hydrogen and oxygen isotopes of local precipitation, leachate samples have a distinctive hydrogen isotope shift toward heavier values. The data show that hydrogen isotope enrichment is strongest during early landfill history, when rates of microbial respiration and methane generation are the greatest. The maximum degree of enrichment is 20 per mil over meteoric water, and lessens with age of waste suggesting that this technique would be most useful for detecting liner leaks early in the operational history.